1. Field of the Invention
This invention relates to methods and apparatus for forming tubular articles, each with one closed end, from thermoformable polymer materials, particularly but not exclusively high molecular weight saturated linear polyester materials such as polyethylene terephthalate.
2. Discussion of the Prior Art
Various proposals have been made in the past for forming such articles by the technique of plug-forming, in which an annular region of a sheet of the polymer material is clamped and the portion of the sheet within the clamped region is heated to a temperature above the glass transition temperature but below the annealing temperature of the polymer material, and a plug heated to a temperature in the same range is forced through the plane of the sheet at a position centred within the clamped region so as to draw the polymer material into the form of a tubular body with a closed end. The speed of travel of the heated plug has generally been quite slow, e.g. of the order of 0.6 to 0.8 cm per second, resulting in a long production cycle time.
It is an object of the present invention to provide methods and apparatus for forming such articles reliably and effectively in relatively short process times.